While the invention has wide application, its use will be described relative to compact fluorescent lamps.
The fluorescent lamp is the most widely utilized light source in the world for general illumination, primarily because of its relatively low initial cost and its efficacy: i.e., its light output relative to its power input, usually expressed as lumens per watt (LPW). Nevertheless, for home use, the fluorescent lamps has not taken precedence over the incandescent lamp. Many reasons have been advanced for this lack of acceptance, among them the poor color rendition of some fluorescent lamps and their need for a ballast. However, one of the major disadvantages lies in the fact that a fluorescent lamp is a linear light source whereas an incandescent lamp can almost be considered a point source. The typical flourescent lamp has a length of from 18" to 8' and is somewhat cumbersome to work with.
With the increasing cost of energy, attempts have been made to overcome the latter difficulty. One of these attempts has utilized a plurality of fluorescent tubes having one or more smaller tubes connecting the ends of the fluorescent tubes to provide an arc path. Such lamps are shown in U.S. Pat. No. 3,501,662. Large, "U" shaped lamps such as those shown in U.S. Pat. Nos. 3,602,755; and 2,401,228; and triple bend lamps such as shown in U.S. Pat. No. 4,347,460 exemplify other attempts.
Still other attempts are shown in U.S. Pat. Nos. 4,208,618; 4,191,907; and Ser. No. 431,955, filed Sept. 30, 1982, now U.S. Pat. No. 4,524,301 assigned to the assignee of the instant invention.
While each of these proposals has its own advantages, disadvantages also exist. The previous forms of multiple tubing lamps are expensive to produce and difficult to handle during manufacture.
Many types require expensive, custom made partitions and/or require large numbers of hermetic seals. Multiple bend tubes require large outlays for manufacturing equipment which adds to the cost of the final lamp.
Recently developed compact fluorescent lamps such as disclosed in U.S. Ser. No. 481,230, filed Apr. 1, 1983, and now U.S. Pat. No. 4,527,089 assigned to the assignee of the instant application, solved many of the above recited disadvantages and the teachings of Ser. No. 481,230 are hereby incorporated herein by reference.
Generally, these lamps comprise an inner lamp assembly mounted within an outer jacket. The inner assembly defines a long arc path in a compact shape and is exposed to an arc generating and sustaining atmosphere contained within the outer jacket. The outer jacket is hermetically sealed but the components of the inner assembly are not. Where necessary, they are fitted in an arc-tight manner but are open to the atmosphere contained within the outer jacket.
To aid in evacuating the inner assembly it has been provided with an exhaust port which can be separately formed in, for example, an arc director. Alternatively, open exhaust tubulations could be employed with the inner assembly.
While this system works well, it has been observed that on occasion the arc will leak from the provided exhaust tubulation and take a path other than that intended.